There are known automatic flow wrapper machines for packaging and sealing packages.
In the normal operation of automatic flow wrapper machines 6 main stations are used.
The infeed station for manual or automatic loading of the product, equipped with interconnected pushers and driven by a chain or by an endless conveyor belt.
The film station for unwinding the material used to wrap the product wrapping from a reel.
The forming station (or folding box) for conveying the film towards the subsequent station, establishing the form of the final bag inside which the packaged product will be contained.
The longitudinal welding station (consisting of one or more pairs of wheels closed at constant pressure and heated to a predetermined temperature) for the first welding of the film, parallel to the surface on which the product slides along its direction of feed, so as to produce a sort of continuous open tunnel.
The transverse welding station (consisting of one or more pairs of jaws closed cyclically under pressure and heated to a predetermined temperature) for the second welding of the film, orthogonal to the direction of feed of the product, so as to produce a closed bag sealed for the whole of its length and at its ends. A shear blade is inserted inside the welding jaws to enable simultaneous separation of two adjacent products.
The outfeed station for ejecting the product packaged in a bag.
The product, loose or transported in supporting containers arriving from the infeed unit, reaches the folding-box forming unit pushed by carriers on a moving chain or conveyed on a specific belt. A photocell detects the presence of the product according to a predefined position and frequency, suitably adjusting the film unwinding speed around the forming unit and the driving speed of the longitudinal sealing wheels, cyclic and instantaneous closing of the transverse sealing jaws is synchronized with feed of the product, ensuring a final package wrapped around the product according to the real length and width measurements.
Each time it is necessary to operate with products that require extended preservation and consequently modified atmosphere packaging (MAP), the tightness of the weld in time under the effect of the internal pressure exerted by the gas mixture is an important element.
The tightness of the tight seal is a very important specification in order to ensure the tightness of the package inside which the product, generally preserved in modified atmosphere, is contained.
The transverse sealing station is particularly important.
There are two solutions relating to the transverse sealing station, namely the rotary type and the box-motion type, based mainly on the coupling of two jaws with opposite and parallel faces between which the packaging film is blocked and welded.
In the first case, the welding period is almost instantaneous, namely the fraction of second in which the two circumferences, described by the trajectories of the ends of its masses, touch in their point of tangency.
An example of a transverse sealing station of rotary type is described in the document EP 1 810 922.
In the second case, the sealing period is longer, as the coupled jaws trace a linear line in space, parallel to the packaging plane and opposite the direction of feed of the product, so that the combination of the sealing path with the jaws closed and the reverse path to return to the initial position with the jaws open defines a parallelepiped in space, giving rise to the term box-motion.
Alternatively, in the D-CAM type solution two distinct movements are performed, namely a translational movement and a rotational movement.
A suitable combination of pressure, temperature and sealing time enables a correct melting process of the adhesive surface of which the film used for packaging is composed.
The temperature and pressure variables depend on the constructional characteristics of sizing, respectively electrical and mechanical, while a somewhat critical variant in this type of application is the sealing time, as it is strictly linked to the production capacity of these machines: high production rates and consequently a high number of cycles implies a proportional reduction in the duration of the period in which the welding surface is heated and pressed at high temperature.
The main criticalities of transverse sealing solutions are largely related to the effect of the mechanical vibrations that derive therefrom.
This leads to lower performance, due to structural and mechanical limits, to mechanical oversizing to make the structure as a whole more stable, to increased complexity in the construction and control of the transverse welding unit, to a consequent increase in the quantity and costs of the materials used, to less flexibility and capacity to adapt to the sizes of the product without significant operations to reconfigure the machine, and to increased complexity in terms of maintenance and cleaning.
Therefore, as it is only possible to act on the sealing time, the pressure and the temperature being closely linked to the constructional and sizing characteristics of the machine, a suitable transverse welding unit must be used.
In the case of Box-Motion and D-CAM solutions, the two welding jaws are forced to perform a sequence of translational movements that transmit strong vibrations to the machine, which it may not be able to withstand mechanically as productivity increases; to date, machines with QS of the Box-Motion or D-CAM type reach a maximum tested productivity of around 100-120 packages per minute.
Therefore, the possibility of tracing a smoother continuous movement in space, not deriving from a sequence of broken lines, but which nonetheless has a certain rectilinear line in which the two jaws are coupled under pressure and at a temperature for an extended (not instantaneous) time would allow the mechanical vibrations on the machine to be limited and an increase in productivity, at this point highly dependent only on the type of material used.